Industry is constantly searching for high temperature stable materials that resist degradation. Such materials can have utility, for example, as adhesives, and in vibration damping applications.
IPNs have been disclosed. Energy-curable compositions comprising interpenetrating polymer networks of epoxy resins and acrylate resins have been described (see, for example, U.S. Pat. Nos. 5,262,232 and 5,086,088) in which the compositions are stated to be useful as pressure sensitive adhesives and as vibration damping materials. However, the compositions have limited utility at higher temperatures.
Cyanate esters, which can be prepared by reacting polyhydric phenols with cyanogen bromide, as described in U.S. Pat. No. 3,553,244, are thermosetting resins having high heat resistance and, at the same time, considerable brittleness. Interpenetrating polymer networks of cyanate ester resins and acrylate resins show considerably increased flexibility as well as resistance to moderately high temperature degradation. See, for example, U.S. Pat. No. 5,331,018. However, industrial applications at temperatures exceeding 275.degree. C. are becoming more common, and the need exists for materials that are both flexible and durable at these temperatures.
Blends of cyanate ester resins and epoxy resins have been described. For example, U.S. Pat. Nos. 4,604,452, 4,785,075, 4,902,752, 4,983,683, 5,068,309, and 5,149,863 describe various blends of cyanate ester resins with glycidyl ethers of polyhydric phenols ('452 and '075) or with thermoplastic resins such as polysulfones, polyetherimides, polyarylethers, etc., terminated with epoxy groups ('752 and '683). Compositions of various morphologies and properties were obtained. Single polymer networks or polymer blends were obtained, but no interpenetrating polymer networks are disclosed.
U.S. Pat. No. 4,797,454 describes cyanate-functional oxazolinylpolysiloxanes useful for toughening resin systems such as epoxies and cyanates. Oligomeric epoxy-terminated siloxanes (e.g., glycidyl ethers) are reacted with dicyanates to give a resin additive, demonstrating that cross-reaction of glycidyl ethers with cyanates is faster than self-condensation of the epoxy compounds, so that no interpenetrating polymer network is formed.
U.S. Pat. No. 4,956,393 describes heat curable cyanate adhesive compositions comprising a cyanate ester resin, an epoxy resin, and a catalyst effective to promote the elevated temperature cure of the composition. Both polysiloxyl and cycloaliphatic epoxy resins are disclosed, while tin catalysts, e.g., tin octanoate, are said to be preferred for the polymerizations (col. 7, lines 8-9). In Example 9, a non-Bronsted acid initiator is used in an uncured composition comprising cycloaliphatic epoxy, cyanate ester, and polyimide.
U.S. Pat. No. 5,043,411 describes a thermosetting cyanate ester resin containing an epoxy resin pre-condensed with an aromatic amine or aromatic amide. As catalyst for the cyanate ester polymerization, only a coordination metal compound soluble in nonylphenol is described. Catalysts for the epoxy condensation reaction include amine salts, imidazoles, tertiary amines or hindered phenols. Interpenetrating polymer networks are not disclosed.
U.S. Pat. No. 5,330,684 describes Z-axis conductive adhesive compositions comprising cyanate ester resins, film-forming thermoplastic resins, epoxy resins including cycloaliphatic epoxies, an organometallic catalyst, and conductive particles. No Bronsted acids are disclosed as catalysts.